Looking at a handful of the stuff you dig up out of a healthy garden, you might be tempted to call it dirt. Don’t! “Dirt” is degraded, lacking nutrients and life. Soil is alive! What does that even mean? When we think about the living things in nature, we don’t often consider what’s underneath our feet. But when you dig up a shovelful of healthy garden soil, you might be surprised to discover that it’s teeming with life. From microscopic organisms to burrowing insects and animals to the roots that spiral their way deep into the ground, there’s a lot going on inside soil and a lot that separates it from dirt.

Components of Healthy Soil

Healthy living soils are made up of several components: pore space, minerals, water, biota, and organic material. Pore space is the air between the particles, which provides oxygen and loft. Healthy soil is porous instead of compact. Minerals, such as feldspar and quartz, are broken-down rock particles that define a soil’s texture and consistency. Water, of course, is necessary for all life on Earth to grow, and it makes up a large percentage of healthy soil – just as it makes up a large percentage of you. 

Bring on the Biota

The living part of “living soil” comes from the final two components: biota and organic material. Biota includes microorganisms, such as bacteria, algae, and fungal spores, as well as larger organisms like protozoa, nematodes, hexapods, insects, spiders, and earthworms that call soil their home. These critters form a complex food web producing, feeding, and breaking down nutrients in the soil. 

Biota are divided into five groups: producers; primary, secondary, and tertiary consumers; and decomposers. Producers (cyanobacteria and blue-green algae) create material within the soil. Primary consumers (protozoa, amoeba, and nematodes) break down that organic matter directly. Secondary consumers (predator nematodes) eat the primary consumers. Tertiary consumers (worms and arthropods) keep populations of primary and secondary consumers at a manageable level, and apex predators (birds) prey on those predators. All of these are broken down after death by decomposers (fungi). In the microbe food web, you can see just how these populations work together.

Let it rot!

Organic material is the final piece of the component puzzle of healthy soil. This includes plant matter, from roots winding their way through the soil to decaying leaves and stems. Organic material feeds the organisms that live within the soil. Eventually, this organic material will break down enough to become nutrients that plants need to grow.

All these components work together as a healthy miniature ecosystem. Fungi decompose decaying plant matter, and tiny organisms feed on the fungi and the organic material. Water moving through soil washes nutrients into areas where living plant roots can pick them up. Pore space allows the biota, roots, and water room to move around. And the minerals found in the rocks that make up the soil release nutrition as they’re weathered by all the other soil components. 

Living soil is important for food systems. It provides fertility, nutrition, and biodiversity to the producer plants growing out of it, which in turn feeds the consumers that rely on those plants.